The present invention relates to a device for controlling the angle of tilt of a frame mounted on a tiltable wheel set.
The field of the invention is thus that of vehicles that include a tiltable frame such as tricycles or quadricycles. With a tricycle, the frame supports one wheel at one of its ends and it is hinged to a wheel set at its other end. With a quadricycle, the frame is hinged between a front wheel set and a rear wheel set. Each wheel set thus comprises two wheels and the present invention relates to sets in which the two wheels are independent and are also tiltable.
Thus, document FR 2 616 405 teaches a motor-driven tricycle having a rear wheel set in which the wheels are independent and tiltable. Each of those wheels is mounted on an oscillating arm also hinged to a transverse shaft secured to the frame. A rocker arm has its center connected to the frame by a shock absorber and has its two ends connected to the two oscillating arms by connecting rods.
It is found that that tricycle does not provide the required level of safety at high speed when negotiating bends. The frame is subjected to centrifugal force that is due essentially to the weight of the rider tending to tilt towards the outside of the turn.
Such a position of the frame makes driving difficult or even dangerous. Furthermore, the rider may nevertheless be caused to make the frame tilt in the wrong direction.
Document WO 2006/130007 describes a tricycle with its tilt angle being motor-driven. The control of this motor drive takes account of a speed sensor, a direction sensor, and a lateral acceleration sensor. It is designed to give precedence to lateral acceleration when stationary or at low speed, whereas at high speed it is the direction sensor that predominates. Once again, the tilt angle of the frame is not really under control at high speed.
Motor drive for the tilt angle interferes with natural riding since it imposes the tilt angle rather than allowing physical phenomena to act, namely weight and centrifugal force. Furthermore, it consumes energy in order to set the tilt angle of the frame, and that is very penalizing in ecological vehicles with low fuel consumption and therefore appears to be practically inapplicable for a human-propelled non-motorized vehicle.
Furthermore, the complete system for controlling tilt angle is rather complex, which is clearly a handicap in terms of vehicle cost.
Thus, document FR 2 825 672 provides a solution for limiting the risk of tilting in the wrong direction. The tricycle has an axle arranged at the rear, a frame that supports the steering wheel at the front, and a hinge for connecting the frame to the axle. However in that document the hinge is passive, with the frame being free to tilt in compliance with the resultant of the forces that are applied thereto. That tricycle also has means for blocking the hinge, which means are controlled by a pendulum member. The objective in that document is to avoid the frame tilting when stationary or at very low speed, and the mechanism is thus deactivated as soon as the speed exceeds a predetermined threshold. The pendulum member presents mechanical structure that is complex and can lead to the frame being jammed suddenly.
Also known is document FR 2 933 950 that provides a satisfactory solution in terms of controlling tilt angle. In that document, a device comprises a chassis, a tiltable frame, a passive hinge enabling the frame to tilt relative to the chassis, and blocking means for blocking the hinge, namely an actuator. Control is performed by means of an accelerometer arranged on the tiltable frame and a control circuit that blocks the actuator when acceleration becomes too great.
Adapting teaching of that document to a wheel set having oscillating arms leads to arranging the blocking means between the frame and the rocker beam, as in document FR 2 550 507. That arrangement does not favor decoupling between the shock absorber and the actuator.
When tilting, it is appropriate to avoid interfering with the free movement of the shock absorber in order to avoid any interference with tilting. Unfortunately, the length of the actuator is a function of the tilt angle: this variation in length opposes free movement of the shock absorber.
When hunting, it is also desirable for there to be no variation in the length of the actuator in order to avoid opposing the shock absorber. Once more the length of the actuator is a function of the length of the shock absorber.